There is known one of optical modules that emit light from laser diodes through an optical fiber. In this optical module, the optical fiber is led out from inside to outside a housing. In the housing, optical components such as the laser diodes, mirrors, a lens, and the optical fiber are arranged. The light emitted from each the laser diodes is condensed and entered into the optical fiber, and is emitted from the optical fiber to the outside of the housing.
For example, Patent Literature 1 below discloses an optical module that includes: a plurality of laser diodes arranged on a stepped mount; mirrors provided corresponding to each of the laser diodes; and a condenser lens that condenses light reflected by each of the mirrors and enters the light into the optical fiber.
Patent Literature 2 below discloses an optical module that includes: a plurality of laser diodes arranged on the same plane; a collimator that collimates light emitted from each of the laser diodes; and diffraction gratings that change the direction of the collimated light; and a condenser lens that condenses the light redirected by each of the diffraction gratings and enters the light into the optical fiber. The laser diodes included in such an optical module are formed by laminating semiconductor layers in a direction perpendicular to the plane on which the laser diodes are arranged. Accordingly, the light emitted from the laser diodes has a slow axis direction parallel to the plane on which the plurality of laser diodes is arranged. In addition, in the optical module described in Patent Literature 2 below, light propagates from each of the laser diodes to the condenser lens in a plane parallel to the plane on which the plurality of laser diodes is arranged. Therefore, in this optical module, the light emitted from the plurality of laser diodes is incident on the condenser lens in parallel to the slow axis direction.    [Patent Literature 1] U.S. Pat. No. 6,124,973    [Patent Literature 2] JP 2015-72956 A
In the optical module as described above, the heat emitted by the laser diodes is transferred to a heat sink via the mount. When a plurality of laser diodes is arranged on a stepped mount as in the optical module described in Patent Literature 1, there occurs a difference in the length of a heat radiation path among the laser diodes. Therefore, the junction temperature is likely to be different among the laser diodes. If there is a difference in the junction temperature among the laser diodes, the laser diodes vary in lifespan, and thus the reliability designing of the optical module may become complicated.
Further, in the optical module described in Patent Literature 2, the light emitted from the plurality of laser diodes is aligned in the slow axis direction as described above. However, the light emitted from the laser diodes is less likely to be collimated in the slow axis direction than in a fast axis. Therefore, in the optical module described in Patent Literature 2, the light emitted from the plurality of laser diodes is hard to condense in a narrow area, which makes it difficult to achieve high output power.